The present invention relates generally to monitoring the medical condition of a woman in labor and in particular to processing abdominal surface electromyogram (EMG) signal data for the purpose of uterine contraction monitoring.
The present technology for monitoring uterine contraction is a tocodynamometer, which measures the abdominal pressure exerted on a belt placed around the lower abdomen of a patient in labor. However, the tocodynamometer can be uncomfortable for some patients to wear. Additionally, abdominal pressure changes can be harder to detect on larger women. Enhanced uterine contraction monitoring is required to provide obstetricians with an improved tool to diagnose whether a patient is at risk of preterm labor. Because premature birth is the leading cause (85%) of infant death, improved EMG technology holds the potential to advance prenatal care and management.
It has been well established that uterine contractions are caused by electrical potentials generated and propagated by muscle cells. These electrical activities occur in bursts and give rise to measurable electric fields called electromygraphic (EMG) signals. The frequency and duration of certain features of the EMG signals correspond to the frequency and duration of the uterine contractions. The temporal and spectral characteristics of an EMG signal, recorded by external electrodes, make it possible to discriminate between efficient and inefficient contractions in terms of electrical command capability. It is also reported that the spectral density of the EMG signals shifts significantly at different stages during gestation, providing a means of separating non-laboring contractions from laboring contractions. It is possible to record uterine electrical activity as early as a gestational age of 19 weeks. Therefore, an abdominal EMG signal can be of value for pregnancy monitoring.
It is known that the EMG signal can be reliably recorded by placing electrodes on the internal uterine surface. However, such a procedure is both invasive and not accepted in clinical use. It has been proposed that the EMG signals should be acquired on the exterior surface of the abdomen, and this procedure has been shown to work in practice. EMG signals acquired from the exterior surface of the abdomen can be used to detect and monitor contractions, due to the relationship between the onset of contraction and the spectral characteristics of the EMG signal. The main obstacles to such a use of EMG technology are, first, patient motion which causes noise and signal artifacts, second, interference from other physiological electrical events (such as Electrocardiogram (ECG)), and, third, imperfect electrode contacts.
There is a need for an effective means of accurately processing the EMG signal from the electrodes attached on the external abdominal wall, in order to extract from it an indication of when the periods of contraction occur.